Production of chlorothiophene



United States Patent PRODUCTION OF CHLOROTHIOPHENE George McCoy,Philadelphia, and Charles Roslyn, Pa., and Glendon D. Kyker, Tenn.,assignors to Pennsalt Chemicals a corporation of Pennsylvania NoDrawing. Application October 4, 1955 Serial No. 538,511

6 Claims. cram-332.5

E. Inman, Chattanooga, Corporation,

This invention relates to the production of chlorothiophenes and moreparticularly to the production of chlorothiophenes substantially free ofchlorinated thiophene addition products.

The present application is a continuation-in-part of pending applicationSerial No. 269,323 and of application Serial No. 269,324, now abandoned,both filed January 31, 1952.

In the preparation of chlorothiophenes it is the practice to directlychlorinate thiophene and then separate the chlorothiophenes from thechlorination product. However, during the chlorination a substantialquantity of chlorinated thiophene addition products are formed,

such addition products at times being as much as 20%- of the chlorinatedproduct depending on the conditions of chlorination. In order toincrease the yield of the chlorothiophenes obtained it has been thepractice to break down these addition products by pyrolysis alone or byheating in the presence of a strong caustic solution such as water oralcoholic solutions of NaOH or KOH. Through this treatment HCl is splitout of the addition product and the corresponding chlorothiopheneformed, the chlorothiophene formed depending on the addition productswhich are dehydrochlorinated. Since the addition products are generallya mixture of compounds such as tetra, penta, and hexa chlorothiolanesand chlorothiolenes, the resulting.chlorothiophenes obtained are amixture of chlorothiophenes. In the mixture of addition productstetrachlorothiolane is generally present in the greatest amount.

Though the overall yield of chlorothiophene may be increased by straightpyrolysis or by heating in the presence of caustic, these proceduresthemselvesare not entirely satisfactory. Where caustic is employed tocause the decomposition of the addition products, the caustic materialtogether with the resulting salts formed must thereafter be removed,Where the decomposition of the addition products is brought about byheat alone, the high temperature necessary to obtain any appreciablerate of decomposition causes the production of undesirable tarrymaterials. Furthermore, the cost of heating the chlorination product tothe higher temperature necessary to cause appreciabledehydrochlorination is objectionable.

We have now discovered that by carrying out the pyrolyticdehydrochlorination of the addition chlorination products in thepresence of activated carbon, the rate of dehydrochlorination to thecorresponding chlorothiophene for any given temperature can besubstantially increased. Also the temperature required to convert theaddition products to chlorothiophene is substantially less when thereaction is carried out in the presence of activated carbon. Thus, forexample, whereas appreciable dehydrochlorination will occur withtetrachlorothiolane, when heated in the presence of activated carbon togive dichlorothiophene, at temperatures as low as 143 C. and

6 2,851,464 Ce Patented Sept. 9, 1958 or greater since at these highertemperatures the dehydrohalogenation is more rapid. There is littleadvantage, however, in going to temperatures much in excess of about 200C. The temperature should preferably not exceed 260 C. since attemperatures much in excess of 260 C. tarry side reaction products tendto form.

In practicing our present invention the thiophene may be chlorinated inany suitable manner. The chlorination proceeds readily and rapidly atroom temperatures. The resulting chlorination product is heated in thepresence of activated carbon to break down the chloro addition productsto the chlorothiophenes which can then, if desired,'be separated byfractionation. The chlorination of the thiophene and the decompositionof the addition products can be carried out simultaneously, if desired,by chlorinating the thiophene in the presence of activated carbon at atemperature in excess of about 143 C.

If the chloro addition product is substantially pure tetrachlorothiolanedehydrochlorination, in the presence of activated carbon as described,will yield substantially pure dichlorothiophene and HCl. The evolvedHCl,

which is preferably absorbed in water after treatment toremove anyentrained organics, may be used or sold as a high quality muriatic acidsince substantially no impurities are present. However, in practicingthe present invention it is generally preferred to treat the reactionmass resulting from the chlorination of thiophene, consisting of amixture of chlorothiophenes and chlorinated thiophene addition products,with activated carbon at elevated temperatures as described, to convertall of the addition products to chlorothiophenes. These chlorothiophenesmay then be separated by fractionation if desired.

The chlorination of thiophene may of course be done in the presence ofactivated carbon, if desired. This may be either at a temperature belowthat required to de- Example 1 10 grams of tetrachlorothiolane washeated in a small distillation flask to 180 C. There was at thistemperature a very slow evolution of HCl from the molten mass. Onaddition of 1 gram of Columbia Activated Carbon SXW, HCl was given oflrapidly. Heating was continued at reflux temperature until no furtherevolution of HCl was apparent. The resulting product on distillationfrom the flask was found, after analysis, to be substantially puredichlorothiophene,

Example 2 5 grams of tetrachlorothiolane was mixed with 5 grams ofdichlorothiophene. treated in the manner described in the precedingexample. The final product, on analysis, was found to be substantiallypure dichlorothiophene.

Example 3 5 grams of hexachlorothiolane was treated in a small flaskequipped with a reflux condenser to 230 C. at which temperaturerefluxing occurred. A small amount of HCl was liberated indicatingslight decomposition of the hexachlorothiolane. 1 gram of ColumbiaActivated Carbon SXW of 6-8 mesh was added. Immediately there was arapid evolution of HCl and the vapor temperature dropped to 175 C. Thistemperature was maintained for a few minutes, but as the amount of HClevolved decreased the temperature slowly rose. After the two hours theHCl evolved was nearly negligible and the temperature had risen to 228C. Further addition of activated carbon caused no further release of HClindicating that the reaction had gone to substantial completion. Theproduct on analysis was found to be tetrachlorothiophene.

Example 4 Thiophene was chlorinated with 2 mols chlorine per molthiophene at a temperature of about 30 C. for one hour. The chlorinationproduct was then heated in the presence of activated carbon at atemperature of 146 to 172 C. in the absence of chlorine for about fourand ahalf hours. The product was then fractionated and found to consist,on the basis of total crude, of about 7% monochlorothiophene, 59%dichlorothiophene, and 30% trichlorothiophene, the remaining 4% beingstill pot hold up which, after collection, was found to be substantiallyfree of any addition chlorination products.

Example 5 Thiophene and chlorine, using about 2 mols of chlorine per molof thiophene, were passed into a zone of activated carbon maintained ata temperatureof about 160 to 180 C. About 43 grams of the resultingproduct was fractionated and on the basis of total crude yielded about44.0% monochlorothiophene, 23% dichlorothiophene, 18% trichlorothiopheneand 11% tetrachlorothiophene. The still pot hold up, which was about 4%as in Example 4, was found to be substantially free of any additionchlorination products.

In describing our invention several examples have been given. Obviously,many variations could be made difiering substantially from the specificexamples given and still utilizing our invention concept in the use ofactivated carbon for converting addition chlorination The resultingmixture was then.

products of thiophene to chlorothiophenes. Many of these willimmediately be apparent to one skilled in the art having the teaching ofthe present specification before them. Also, activated carbons otherthan those specifically mentioned can be employed. The invention,therefore, should not be limited to any specific illustration orillustrations which may havebeen employed to aid in its presentation,but should be interpreted only in the light of the full disclosure andthe prior art.

Having thus described our invention, we claim:

1. The process of making dichlorothiophene comprising the step ofheating tetrachlorothiolane in the presence of activated carbon at atemperature of at least 143 C. but not substantially above 260 C.

2. The process of making tetrachlorothiophene comprising the step ofheating hexachlorothiolane in the presence of activated carbon to atemperature of at least 143 C. but not substantially above 260 C.

3. The process of converting chlorine addition products of thiopheneresulting from the addition of chlorine to the thiophene ring tochlorothiophenes comprising the step of heating said addition productsin the presence of activated carbon to a temperature of at least 143 C.but not substantially above 260 C.

4. The process of claim 3 wherein said temperature is within the rangeof about 160 to 260 C.

5. The process for preparing chlorothiophenes substantially free ofchlorine addition products resulting from the addition of chlorine tothe thiophene ring comprising the steps of heating the reaction productproduced by ring-chlorinating thiophene to a temperature of at least 143C., but not substantially above 260 C. in the presence of activatedcarbon.

6. The process of preparing chlorothiophenes comprising the step ofring-chlorinating thiophene in the presence of activated carbon at atemperature of at least 143 C., but not substantially above 260 C.,thereby effecting simultaneously with the chlorination reaction, thedehydrochlorination of chlorine addition products resulting from theaddition of chlorine to the thiophene ring.

References Cited in the file of this patent FOREIGN PATENTS 108,424Austria Dec. 27, 1927 503,063 Belgium Nov. 5, 1951 955,816 France July4, 1949 420,500 Germany Oct. 24, 1925 OTHER REFERENCES Van Loon: Rec.trav. Chim. 56: 815-38 (1937) (pp. 819 and 835 in particular).

Hartough: Thiophene and Its Derivatives, page 169 (1952).

1. THE PROCESS OF MAKING DICHLOROTHIOPHENE COMPRISING THE STEP OFHEATING TETRACHLOROTHIOLANE IN THE PRESENCE OF ACTIVATED CARBON AT ATEMPERATURE OF AT LEAST 143* C. BUT NOT SUBSTANTIALLY ABOVE 260*C.